(CNN) -- When Alden Waters gets migraines, she feels as if her head is being squeezed into a vise. Depending on what she has eaten, she may vomit. The headache takes longer to go away if she can't rest and goes to teach her math classes anyway.

"It's rare, but it does happen that I won't be able to come to school," said Waters, 26, a Ph.D. student at the University of California, Los Angeles.

About 29.5 million Americans experience migraine pain and symptoms, and 75% of people with migraines are women, according to the federal Office on Women's Health. One of those women is Republican presidential candidate Michele Bachmann, who released a letter from her physician Wednesday explaining her migraine headaches.

Bachmann does not take daily medications to manage her condition, but is prescribed sumatriptan and odansetron for migraines as needed, Attending Physician of the United States Congress, Dr. Brian Monahan, wrote in the letter.

The experience of having a migraine is individual, and it's impossible to generalize about what it feels like for any given person, but many people experience more than just pain in their heads, doctors say.

"Migraine isn't headache. That is a prevalent misconception. It is a state of the brain. Headache is one of many symptoms that reflect that brain state," said Dr. Robert Shapiro, professor of neurology at the University of Vermont College of Medicine.

Throbbing or pulsing in one area of the head typically comes with a migraine. But other symptoms may include nausea and vomiting. Also, people often find that light, sound, movement, touch, taste or smell become magnified or distorted, Shapiro said. There may also be disturbances in thinking or communication.

Sometimes the pain of a migraine can become so severe that it lasts for hours to days, and you just want to lie down in a quiet, dark place.

You may experience "aura," or symptoms that come before the migraine such as flashes of light, blind spots or tingling in the arm or leg.

Research has shown that $20 billion in wages is lost because of migraines, Shapiro said. And some people try to work through their migraines, but most sufferers are about half as productive when in the throes of an attack.

"It remains an enormous source of hidden disability," Shapiro said.

The physiological cause of migraine is still somewhat mysterious, although there seems to be a swelling of the brain's blood vessels, which press on nearby nerves and incite pain.

"Pain itself doesn't come from the brain," Azizi said.

Migraines are also related to genes, and the condition can run in families. Waters, her mother and -- to a lesser extent -- her brother all get migraines.

Medications, both over the counter and prescription, reportedly help a lot. Resting in a dark room can also help.

Going to the hospital may be necessary if the migraine persists for a whole day despite oral medicines. Hospital staff can provide intravenous pain medications and nausea treatments if needed, but it is rare that hospitalization is required, said Dr Ausim Azizi, chairman of the department of neurology at Temple University School of Medicine.

There are specific triggers for migraines but they vary according to the individual person.

Stress can bring them on. A healthy diet, regular exercise, relaxation and good sleep can all help prevent stress that may lead to migraines.

Many women also have migraines right before, during or after their periods.

Particular foods and smells can also trigger migraines, Azizi said. Red wine and chocolate are problematic for some people, as is the smell of perfume.

For Waters, the smell of Asian food is enough to make her start to feel sick. And she knows from experience that eating a lot of salty foods around her period can also lead to problems, so she tries to limit salt intake and doesn't eat at restaurants two nights in a row.

Waters, one of few women pursuing a Ph.D. in theoretical mathematics at her school, feels as though people around her don't really understand how serious migraines are.

Once, at a mandatory teacher training, the smell of cheap pizza was enough to make her feel nauseated, and she asked to be excused. The woman running the training said she would have thought Waters was lying, but knew about migraines because the department secretary also gets them.

"People that know me really well know that I'm not making it up, but I don't think it's a very accepted condition," she said.